For words that only have 3 letters, there isn't any 4th letter. One example is with the word “add”, there aren't any a lot more letters afterwards and thus should be the word "increase". The word “addict” is in the BIP39 wordlist however, you might have utilized “addi” for “addict”. https://bookmarksoflife.com/story4387980/the-ultimate-guide-to-bip39-seed-phrase-github